The liquid phase selective oxidation of olefins, such as propylene, to epoxides using oxygen sources other than molecular oxygen, like hydrogen peroxide, tert-butyl peroxide (TBHP), ethylbenzene peroxide (EBHP), and cumene hydroperoxide is known and can be performed by utilizing homogeneous and heterogeneous catalysts, such as molybdenum compounds or titanated silica, which can be used to produce epoxides along with one or more co-products. These coproducts, such as tert-butyl alcohol in the case of TBHP, or methylbenzyl alcohol in the case of EBHP, are not always desirable. It would be desirable to have a co-product-free process for producing epoxides, such as propylene oxide. Conceptually, this can be accomplished by utilizing molecular oxygen.
Gas phase epoxidation utilizing molecular oxygen, for example, gas phase epoxidation of ethylene in the presence of a silver-containing catalyst at 200-300° C., is known. However, epoxidation of olefins other than ethylene in the gas phase is difficult due to low process selectivity of the reaction associated with the presence of reactive hydrogen atoms in the allylic position to the double bond.
An ongoing need exists for systems and methods for selective epoxidation with molecular oxygen; desirably such systems and methods enable selective oxidation in the liquid phase, which selective oxidation may be continuous.